Micromechanical sensors having a diaphragm are used as radiation detectors, for example, for measuring infrared radiation in gas sensors or as pressure sensors. The micromechanical diaphragms are generally produced by etching a cavern from the back side of the machined wafer down to a dielectric layer by using potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH). Several sensors are formed in one wafer and then separated by cutting the wafer.
More recent approaches begin with etching a cavern beneath the dielectric layer from the front side of the wafer. To do so, the layer is perforated to allow the etching medium such as chlorine trifluoride (ClF3) to have access to the substrate material.
However, the etching front of the cavern is not smooth but instead has peaks due to the undercutting, which begins at the perforation. The diaphragm is put under tensile stress during the etching process to prevent bulging. The tension increases greatly at peaks in the etching front, which may result in cracks in the diaphragm. The development of local stress peaks during the etching process is hardly subject to regulation in particular because of the technically induced fluctuations. Therefore, damage may occur during manufacture, and a substantial portion of the sensors thus manufactured may be defective.